Vibrational circular dichroism (VCD) and vibrational linear dichroism (VLD) are sensitive spectroscopic probes of molecular structure that reveal detailed information about the spatial and stereo-specific organization of matter at the molecular level. The great technological advances of our age, for the genomic and proteomic revolutions in biology, and the miniaturization of electronics and new materials of physics and chemistry, depend on our understanding of matter at the level of individual molecules. As our understanding of the world at this level grows deeper, our ability to control our environment, our communications, and our health increases dramatically.
Despite the usefulness of VCD and VLD, the measurement of these spectra is associated with poor signal-to-noise (S/N) ratios because of the small spectral intensities often associated with such difference in measurements. As a result, novel methods of improving S/N ratios in these measurements are of considerable interest as a result of making such measurements faster and/or of higher quality.
This is particularly true for Fourier transform (FT) infrared VCD (FT-VCD), i.e., the difference in absorbance of a molecule for left versus right circularly polarized radiation, where intensities are commonly in the range 10−4 to 10−6 absorbance units. See Nafie (1997), Ann. Rev. Phys. Chem., 48:357; Nafie (1999) in Encyclopedia of spectroscopy and Spectrometry, J. C. Lindon, G. E. Trantor, J. L. Holmes, Eds. (Academic Press, Ltd., London), p. 2391; Dukor and Nafie (2000), in Encylopedia of Analytical Chemistry: Instrumentation and Applications, R. A. Meyers, Ed. (John Wiley and Sons, Chichester), p. 662; Nafie and Freedman (2000), in Circular Dichroism: Principles and Applications, Second Edition, K. Nakanishi, N. Berova, R. Woody, Eds. (Wiley-VCH, New York), p. 97; Nafie and Freedman (2000), in Infrared and Raman Spectroscopy of Biological Materials, H.-U. Gremlich, B. Yan, Eds. (Marcel Dekker, Inc., New York), p. 15; Nafie et al. (2002), in Handbook of Vibrational Spectroscopy, J. M. Chalmers, P. R. Griffiths, Eds. (John Wiley & Sons, Chichester,), p. 731; and, Nafie (2000), Appl. Spectrosc. 54:1634. S/N is also problematic for another form of spectroscopic measurement, Fourier transform vibrational linear dichroism (FT-VLD).
An obvious way to improve signal quality in such situations is to increase the instrumental throughput for a given spectral region of measurement. However, high throughput presents only a limited solution to S/N problems, in light of detector non-linearity at high infrared intensity levels.
There is therefore a need for methods and instruments for improving S/N ratios in FT-VCD and FT-VLD determinations. The present invention addresses this need for FT-VCD and FT-VLD determinations. The present invention additionally addresses the need for circular and linear dichroism determinations at wavelengths other than the infrared, e.g., at visible/ultra-violet wavelengths.